FIG. 1 illustrates a MEMS switch 10 formed on a semiconductor substrate 12. The MEMS switch 10 includes an actuation member 14, such as the illustrated cantilever, which is formed from a conductive material. The actuation member 14 may have an anchored end 16, an arm 18, and a contact portion 20. The anchored end 16 is attached and electrically coupled to an anchor pad 22 defined on the semiconductor substrate 12. The contact portion 20 of the actuation member 14 forms or is provided with a contact area 24, which is suspended over another contact area 26 on a contact pad 28. The distance between the contact area 24 on the contact portion 20 of the actuation member 14 and the contact area 26 on the contact pad 28 defines a contact gap 30. To actuate the MEMS switch 10 and in particular to cause the actuation member 14 to move the contact area 24 into electrical contact with the contact area 26 of the contact pad 28, an actuator plate 32 is disposed under the arm 18 of the actuation member 14. The distance between the arm 18 and the actuator plate 32 defines an actuator gap 33.
Referring now to FIG. 2, to actuate the actuation member 14 from the open position (illustrated in FIG. 1) to the closed position, a potential is applied to the actuator plate 32 which creates an electromagnetic field. The electromagnetic field exerts a force on the actuation member 14, moving it toward the substrate 12 and thus, moves the contact area 24 on the contact portion 20 of the actuation member 14 into electrical contact with the contact area 26 of the contact pad 28 thereby electrically connecting the anchor pad 22 to the contact pad 28.
FIG. 3 and FIG. 4 illustrate a prior art method of manufacturing the MEMS switch 10 on the semiconductor substrate 12. In FIG. 3, the anchor pad 22, the contact pad 28, and the actuator plate 32 are formed on the semiconductor substrate 12 and a sacrificial layer 34 is placed and patterned over the anchor pad 22, the contact pad 28, and the actuator plate 32. This sacrificial layer 34 forms the mold for the actuation member 14 and includes a recess 36. This recess 36 is shaped to mold the contact portion 20 (illustrated in FIGS. 1 and 2) of the actuation member 14.
Next, referring to FIG. 4, the actuation member 14 is formed over the sacrificial layer 34 and the contact portion 20 is molded by the recess 36 which may also cause the top of the contact portion 20 on the actuation member 14 to have a recess 38. The recess 36 in the sacrificial layer 34 defines the size of the contact gap 30 because the depth and shape of the recess 36 determines the distance between contact area 24 and contact area 26 on the contact pad 28. Similarly, the portion of the sacrificial layer 34 between the actuator plate 32 and the arm 18 defines the size of the actuator gap 33. The sacrificial layer 34 is etched away to form the MEMS switch 10 illustrated in FIG. 1.
Unfortunately, it is difficult to precisely control the shape and depth of recess 36 formed in the sacrificial layer 34. This results in unacceptably high variations in the size of the contact gaps 30 among MEMS switches 10 manufactured in accordance with the prior art method. These variations can reduce the life and performance of the MEMS switch. For example, if the contact gap in the MEMS switch is too small, an excessive amount of force is placed on the contact areas 24, 26 thereby reducing the overall life of the MEMS switch 10. On the other hand, if the contact gap is too large, the contact areas 24, 26 may not properly close the MEMS switch. Another disadvantage of the prior art method is that the recess 36 often is not sufficiently planar thereby causing the contact area 24 on the actuation member 14 to be formed with a low degree of planarization. Also, the sacrificial layer 34 is generally a polymer based sacrificial layer that leaves carbon based contaminants on the contact areas 24, 26. Low degrees of planarization in the contact area 24 of the actuation member 14 and carbon based contaminants can increase the contact resistance and reduce the performance of the MEMS switch 10.
Thus, what is needed are methods and devices for manufacturing MEMS switches that can more easily control and thereby reduce variations in the size of the contact gap. In addition, methods and devices are needed which can provide a higher degree of planarization in the contact area of the actuation member and reduce carbon based contamination in the contact areas of the MEMS switch.